Production of isobutylene polymers, called polybutenes, from mixed C.sub.4 hydrocarbon feedstreams is generally known in the art. It is also known to utilize AlCl.sub.3 as the polymerization catalyst in such processes and the prior art discloses a number of co-catalysts or catalyst promoters for use under various conditions in isobutylene polymerization. Organic nitro compounds are disclosed as components of catalyst systems for polymerization of olefins in concert with AlCl.sub.3 and other components.
U.S. Pat. No. 3,629,222 discloses a process for production of solid, crystalline monoolefinic hydrocarbons such as highly crystalline polypropylene, the polybutenes and polystyrene. The process of the invention results in solid polymers having molecular weights greater than 1,000 and usually greater than 10,000, and can result in polymers of molecular weights of 1,000,000 or higher. The catalyst comprises (1) a compound selected from the group consisting of halides and lower alkoxides of a transition metal selected from the group consisting of titanium, zirconium, vanadium, chromium and molybdenum, (2) at least one component selected from the following: (a) a metal from Groups Ia, II or IIIa, or derivatives thereof; (b) organo-aluminum halides; and (c) a polymeric reaction product of aluminum and a methylene halide, and (3) a third component which can be an organic nitro compound such as nitrobenzene or 2-nitropropane. Polymers obtained by use of the above catalyst are characterized by unusually high crystallinity. There is no disclosure or teaching relevant to preparation of a viscous, liquid polymer characterized by a predominance of vinylidene structures, or use of a catalyst consisting essentially of aluminum chloride and an organic nitro compound.
U.S. Pat. No. 4,027,087 discloses a method for producing ethylene polymers in the presence of a catalyst prepared by using a metal carbonate or/and a metal hydrogen carbonate, a trivalent metal halide, such as AlC1.sub.3, an aromatic compound such as nitrobenzene, a transition metal compound and an organoaluminum compound. The process is suitable for polymerizing alpha olefins other than ethylene but is particularly suitable for polymers of ethylene. The reference teaches all components of the catalyst are essential, that if any one is deficient, a highly active catalyst cannot be obtained.
U.S. Pat. No. 4,103,078 discloses a method for producing polymers of alpha olefins in the presence of a catalyst obtained by mixing an oxide of a metal of I, II, III, VII or VIII Group of the Periodic Table, or SiO.sub.2 or B.sub.2 O.sub.3, with a trivalent metal halide, such as AlCl.sub.3, reacting the resultant mixture with a transition metal compound such as TiCl.sub.4 in the presence of an aromatic compound such as xylene, and activating the resultant reaction product with an organoaluminum compound. The aromatic compound can be nitrobenzene. The monomer can be butene-1. The reference teaches that each component of the catalyst is an indispensable element if a polymerization catalyst with high activity is to be obtained. Polymerization of butene-1 yielded a white polymer of intrinsic viscosity in tetralin at 130.degree. C. of 1.84. Conversion of butene-1 was 69%.
The prior art also discloses a number of co-catalysts, or catalyst promoters, with AlCl.sub.3 for use under various conditions in isobutylene polymerization. A typical co-catalyst is hydrogen chloride. Representative disclosures include U.S. Pat. Nos. 3,200,169; 3,200,170; 3,997,129; 3,985,822; 3,119,884; and 4,558,170.
The present invention is considered distinguished from the foregoing references in that a viscous, liquid polybutene of approximately 50 wt. % vinylidene content is produced by a process wherein the catalyst and co-catalyst consist essentially of AlCl.sub.3 and a liquid, organic nitro compound capable of solubilizing AlCl.sub.3, selected from the group consisting of nitrobenzene, liquid alkyl-substituted nitrobenzene compounds, and aliphatic, liquid alkyl-substituted nitro compounds wherein the alkyl group has from 1 to 6 carbon atoms. Preferably, the aliphatic liquid alkyl-substituted nitro compounds are nitromethane, nitroethane, and nitropropane. The organic nitro compound is unreactive with aluminum chloride and does not neutralize the Lewis acid. The present invention is also considered distinguished from the foregoing references in that it produces a viscous, liquid polybutene which has a relatively high degree of reactivity with anhydrides, such as the reaction of polybutenes with maleic anhydride to produce polybutenylsuccinates.
Polybutenes produced by the process of this invention are characterized by a vinylidene distribution of at least 50 wt. %, and presence of approximately equal amounts of tri-substituted and tetra-substituted olefinic structures. Polybutenes produced by the method of this invention also demonstrate a weight average molecular weight, Mw, within the range of from about 1,000 to about 10,000, which is obtained without need for incremental process cooling facilities to control process temperature, as is required by prior art processes. The increased molecular weight obtained is especially advantageous in preparation of polybutylsuccinates. The higher molecular weight can impart viscosity index improving properties to the final products. The process is further notable in that (1) HCl is not used as a co-catalyst and that (2) the organic nitro compound co-catalyst solubilizes AlCl.sub.3 and permits handling of the AlCl.sub.3 catalyst as a fluid with attendant safeguards. It is equally notable as compared to the relative safeguards required by polmerization processes using boron trifluoride as a catalyst.
It has now been found that polymerization of a butane-butene stream can be carried out at a temperature within the range of from about -20.degree. C. to about +50.degree. C. at a pressure to maintain the feedstream in a liquid state wherein the resulting product has a vinylidene content of at least 50 wt. %.
It has now been found that use of a catalyst comprising aluminum trichloride and a liquid organic nitro compound capable of solubilizing AlCl.sub.3, selected from the group consisting of nitrobenzene, liquid alkyl-substituted nitrobenzene compounds, and aliphatic, liquid alkyl-substituted nitro compounds wherein the alkyl group has from 1 to 6 carbon atoms, preferably nitromethane, nitroethane, or nitropropane, is effective for producing polybutene polymers containing at least 50% vinylidene structure and having a weight average molecular weight range from about 1,000 to about 10,000.
It has now been found that use of an aluminum trichloride and an organic nitro compound as catalyst is effective for producing a polybutene polymer having at least a 50% vinylidene content at a temperature within the range of from about -20.degree. C. to about +50.degree. C.
The present invention is based on the above discovery and relates to an improved method for producing a polybutene with improved unsaturated characteristics. The resulting product has increased vinylidene content and consequently greater utility as a chemical intermediate. Polybutene derivates are useful as additives to lubricants, for example, polybutenes which are reacted with maleic anhydride to prepare polybutenylsuccinate, a motor oil dispersant.